Electron devices employing free space transport of electrons are known in the art and commonly utilized as information signal amplifying devices, video information displays, image detectors, and sensing devices. A common requirement of this type of device is that there must be provided, as an integral part of the device structure, a suitable source of electrons and a means for extracting these electrons from the surface of the source.
A first prior art method of extracting electrons from the surface of an electron source is to provide sufficient energy to electrons residing at or near the surface of the electron source so that the electrons may overcome the surface potential barrier and escape into the surrounding free-space region. This method requires an attendant heat source to provide the energy necessary to raise the electrons to an energy state which overcomes the potential barrier.
A second prior art method of extracting electrons from the surface of an electron source is to effectively modify the extent of the potential barrier in a manner which allows significant quantum mechanical tunneling through the resulting finite barrier. This method requires that very strong electric fields must be induced at the surface of the electron source.
In the first method the need for an attendant energy source precludes the possibility of effective integrated structures in the sense of small sized devices. Further, the energy source requirement necessarily reduces the overall device efficiency since energy expended to liberate electrons from the electron source provides no useful work.
In the second method the need to establish very high electric fields, on the order of 1.times.10.sup.7 V/cm, results in the need to operate devices by employing objectionably high voltages or by fabricating complex geometry structures.
Accordingly there exists a need for electron devices employing an electron source which overcomes at least some of the shortcomings of the electron sources of the prior art.